Twin-screw extruder

Structure and Type

The twin‑screw extruder consists of a drive unit, feeding device, barrel, screws and several other components. The functions of each component are similar to those of a single‑screw extruder. The difference from the single‑screw extruder is that the twin‑screw extruder is equipped with two parallel screws housed within a barrel of "∞"‑shaped cross‑section.

Twin‑screw extruders for profile extrusion are usually closely intermeshing and counter‑rotating. Although co‑rotating twin‑screw extruders are used in a few cases, they generally operate at relatively low screw speeds of approximately 10 r/min.

High‑speed intermeshing co‑rotating twin‑screw extruders are applied for compounding, degassing or as continuous chemical reactors. The maximum screw‑speed range for such extruders is 300‑600 r/min.

Non‑intermeshing extruders are used for mixing, degassing and chemical reactions. Their conveying mechanism differs greatly from that of intermeshing extruders and is relatively close to the conveying mechanism of single‑screw extruders, notwithstanding their essential differences.

Working Principle

From the perspective of motion principle, co‑rotating intermeshing, counter‑rotating intermeshing and non‑intermeshing types differ in twin‑screw extruders.

1、Co‑rotating Intermeshing Twin‑screw Extruders This type of extruder is available in low‑speed and high‑speed versions. The former is mainly used for profile extrusion, while the latter is for special polymer processing operations.

(1) Closely Intermeshing Extruder. Low‑speed extruders feature closely intermeshing screw geometry, in which the flight profile of one screw closely matches that of the other, namely conjugate screw profile.

(2) Self‑cleaning Extruder. High‑speed co‑rotating extruders adopt closely matched flight profiles. Such screws can be designed with fairly small screw clearances to achieve enclosed self‑cleaning performance. This kind of twin‑screw extruder is referred to as closely self‑cleaning co‑rotating twin‑screw extruder.

2、Counter‑rotating Intermeshing Twin‑screw Extruder The gap between the screw channels of a closely intermeshing counter‑rotating twin‑screw extruder is very small (much smaller than that of co‑rotating intermeshing twin‑screw extruders), so positive conveying characteristics can be achieved.

3、Non‑intermeshing Twin‑screw Extruder The centre‑to‑centre distance between the two screws of a non‑intermeshing twin‑screw extruder is greater than the sum of the radii of the two screws.

Product Model